Ionones do this (the smell of violets). Here is a quote and several articles about them:
One quirk of some violets is the elusive scent of their flowers. Along with terpenes, a major component of the scent is a ketone compound called ionone that temporarily desensitises the receptors in the nose; sniff all you like, you won’t get any more smell from the flower.
"Fragrance: The sweetness of violets"
"Sweet and Powdery Fragrance Ingredients: Ionones"